1. Field of Invention
The present invention relates to a charger, and more particularly to a universal charger which is capable of conveniently charging a wide variety of rechargeable batteries through conventional USB ports.
2. Description of Related Arts
A conventional charger usually comprises a charger housing having a battery compartment formed thereon and a power plug extended from the charger housing, and a charging circuitry provided within the charger housing to electrically connect between the power plug and the battery compartment. When a rechargeable battery, such as a cellular phone battery, is placed in the battery compartment, a user can electrically connect the power plug to an external AC power source for charging the rechargeable battery received in the battery compartment.
A main disadvantage of this conventional charger is the need to have an external AC power source for charging the rechargeable battery. Strictly speaking, therefore, the conventional charger is not portable in the sense that the user is usually not able to use it in outdoor environment where an external AC power source is not available. Moreover, the conventional charger is only suitable for one particular type of rechargeable battery. If the user has a number of electronic devices (such as a cellular phone and a camera or a video recorder), he or she has to bring two separate chargers for charging the electronic devices.
In order to resolve this limitation, a number of variations for the above conventional charger have been developed. For example, some chargers have been developed to allow rechargeable batteries to be recharged through USB port. However, those USB chargers have several limitations. First, almost all USB chargers have a rather limited maximum charging capacity, so that they are only capable of charging rechargeable batteries of around 4V capacity. This limitation is due to limited voltage output of a typical USB port of a typical computer. In other words, one may not charge a wide range of rechargeable batteries by a conventional USB ports, because of its inadequate voltage output, and this problem cannot be resolved by buying a new computer, since the power output for a typical USB port of a typical computer is standardized by computers' manufacturers.